Lead-acid battery construction

ABSTRACT

Batteries comprise a carbon fibre electrode construction of the invention and have improved DCA and/or CCA, and/or may maintain DCA with an increasing number of charge-discharge cycles, and thus may be particularly suitable for use in hybrid vehicles.

FIELD OF THE INVENTION

The invention relates to an improved battery construction for lead-acidbatteries particularly but not exclusively automotive batteries forhybrid vehicles.

BACKGROUND

A Pb-acid battery stores and releases energy by electrochemicalreaction(s) at the surfaces of its electrodes. Each cell in the fullycharged state contains electrodes of elemental lead (Pb) and lead (IV)dioxide (PbO₂) in an electrolyte of dilute sulfuric acid (H₂SO₄). In thedischarged state both electrodes turn into lead (II) sulfate (PbSO₄) andthe electrolyte loses its dissolved sulfuric acid and becomes primarilywater. In the pasted-plate construction each plate consists of a leadgrid initially filled with a paste comprising a mixture of leady oxide(Pb and PbO) and dilute sulfuric acid. This construction allows the acidin the paste to react with the leady oxide inside the plate during cellformation (first charge and discharge cycle during which linkages occurbetween neighbouring particles), increasing the electrical conductivityand active surface area and thus the battery capacity. The paste mayalso contain carbon black, blanc fixe (fine barium sulfate), andlignosulfonate.

Vehicle hybridisation driven by increasing worldwide demand for lowerautomotive emissions and/or increased fuel economy places increaseddemand on vehicle batteries, which are most commonly Pb-acid batteries.For example the European Union has set a long-term emissions target ofnot more than 95 g carbon dioxide/km to be reached by 2020 for newvehicles.

Many new internal combustion engine (petrol, diesel, or gas) poweredvehicles also have idle elimination functionality—the engine is arrangedto switch off when the vehicle is stationary or travelling at low speed.Such vehicles are referred to as stop-start vehicles or micro-hybridvehicles. Each engine restart draws energy from the battery and if thisoccurs more quickly than energy can be replaced by recharging, duringonly relatively short engine on periods in commuter traffic for example,the battery charge (or state of charge) will not be maintained. Currentis also drawn from the battery during periods in which the vehicleengine is off to maintain other functionalities in the vehicle such asair-conditioning, radio etc (referred to as “hotel loads”). Batterycharge may fall sufficiently that the vehicle battery management systemwill then override the idle elimination functionality to prevent anyfurther engine stop-starts until the battery's state of charge hasrecovered. Thus to maintain battery charge in even for example heavycommuter traffic a battery for such a stop-start or micro-hybrid vehicleshould have a high dynamic charge acceptance (DCA) rate, which refers tothe rate at which a battery will accept charge.

Vehicles with a higher level of hybridisation including vehiclescomprising both an internal combustion engine and an electric motortypically comprise regenerative braking, in which braking force isapplied by a generator the electric energy from which is stored in thevehicle battery. The vehicle battery is charged only by current fromregenerative braking during time periods in which the internalcombustion engine which also drives a generator (which here includesalternator) is not operating. Under regenerative braking relatively highcharging currents are supplied to the vehicle battery for short timeperiods and thus batteries for hybrid vehicles with regenerative brakingshould also have high DCA. Full electric vehicles also compriseregenerative braking.

The charging system of a hybrid vehicle is arranged to use theengine-driven generator to maintain the charge state of the vehiclebattery at less than full charge such as for example at about 80%charge, so that there is generally capacity available to acceptadditional charging energy from regenerative braking. However thebattery DCA then typically declines over time with increasing number ofdischarge and charge (to less than full charge) cycles, with AGMbatteries typically operating at around 0.1 to 0.3 A/Ah (or 0.1 to 0.3C) within a few thousand cycles. This loss in charge acceptance reducesthe fuel saving capability of the vehicle; automakers ideally want abattery that can accept up to 2 A/ah, or even 3 A/Ah over a 5 to 10second period to maximise the fuel saving potential of the start/stopand regenerative braking functions. However, any improvement above the0.1 to 0.3 A/Ah is a valuable improvement. Typically the charging systemof a hybrid vehicle is arranged to allow the battery to discharge andthen (using the engine-driven generator to) charge the battery.Generally, the cars Battery Management System will periodically fullycharge the battery (or “recondition” the battery) to restore the batteryDCA, such as every three months. An ideal Pb-acid battery, particularlyfor a hybrid vehicle, would maintain DCA without requiring periodic fullcharging, or at least would maintain a higher rate of DCA betweenreconditioning cycles.

In a Pb-acid battery DCA is primarily determined by the chargingreaction at the negative electrode.

A battery should also meet other requirements, such as have highvolumetric energy density. Volumetric energy density (VED) refers to theenergy supplied per unit volume of electrode. A closed Pb-acid batterysystem should also have low water consumption. And an automotive batteryin particular should be able to deliver high current for enginestarting, at low temperature. A cold cranking amps (CCA) test tests theability of a battery to do so.

U.S. Pat. No. 7,569,514 describes utilising activated carbon as anelectrode in an absorbed glass mat battery to overcome sulphation tothereby increase the dynamic charge acceptance of the battery.

U.S. Pat. No. 4,429,442 describes a lead-acid battery plate comprising ametal grid and active mass and a layer of carbon fibrous material on theside of the active mass to enhance mechanical integrity of the activemass.

U.S. Pat. No. 4,342,343 describes a negative lead-acid storage batteryplate with interconnected carbon fibres over the face of a pasted plate.During manufacture formability is enhanced by securing the fibres to apaper carrier and then pressing the same to the plate.

U.S. Pat. No. 6,617,071 describes an electrode having a conductivepolymeric matrix formed over the surface of a grid plate where theconductive polymeric matrix comprises superfine or nanoscale particlesof active material.

Our international patent application publication WO2011/078707 disclosesa lead-acid battery comprising as a current collector a conductivefibrous material of filaments with low interfibre spacing and conductingchains of Pb-based particles attached to the fibres, which providesimproved battery performance particularly DCA.

SUMMARY OF INVENTION

It is an object of at least some embodiments of the invention to provideimproved or at least alternative electrodes and/or cells and/orbatteries particularly but not necessarily exclusively suitable for usein hybrid vehicles, and/or methods for manufacturing same.

In broad terms in one aspect the invention comprises a lead-acid batteryor cell including at least one (non-composite or composite) electrodecomprising as a current collector a conductive fibrous materialcomprising, when fully charged, voidage (being the fractional volumeoccupied by the pores between the lead and conductive fibres) of betweenabout at least about 0.3, and a mass loading ratio of lead (in whateverform) to the mass of conductive fibres, when converted to volume ratio,in the range about 0.7:1 or about 1:1 to about 15:1 or about 10:1 (eachover at least a major fraction of the electrode and more preferably oversubstantially all of the electrode).

In broad terms in another aspect the invention comprises a method formanufacturing a lead-acid battery or cell which includes forming atleast one (non-composite or composite) electrode comprising as currentcollector a conductive fibrous material comprising when fully charged,voidage (being the fractional volume occupied by the pores between thelead and conductive fibres) of at least about 0.3, and, a mass loadingratio of lead to the mass of conductive fibres, when converted to volumeratio in the range about 0.7:1 or about 1:1 to about 15:1 or about 10:1.

In some embodiments the voidage is between about 0.3 and about 0.9,about 0.3 and about 0.85, more preferably between about 0.3 and about0.8, more preferably between about 0.5 and about 0.98, furtherpreferably between about 0.8 and about 0.95.

In some embodiments the volume loading ratio of the active material whenconverted to Pb to conductive fibres is between about 0.7:1 or about 1:1and about 7:1, or about 1.5:1 and about 5:1, or about 2:1 and about 4:1.

Typically the voidage may be present as corridors to form between thelead and carbon to enable lead particles to form between each of thecarbon fibres. In some embodiments the average spacing betweenconductive fibres is between about 0.5 and about 10, more preferablybetween about 1 and about 5 fibre diameters. In some embodiments theaverage interfibre spacing between fibres is less than 50 microns orless than 20 microns. Preferably said average interfibre spacing is overat least a major fraction of the material and more preferably oversubstantially all of the material. In preferred embodiments the averagefibre diameter is less than about 20 or less than about 10 microns.

In broad terms in another aspect the invention comprises a lead-acidbattery or cell including at least one (non-composite or composite)electrode comprising as a current collector a conductive fibre materialcomprising, when fully charged, voidage (being the fractional volumeoccupied by the pores between the lead and conductive fibres) of atleast about 0.3 and a loading ratio of the volume of lead (in whateverform) to the volume of conductive fibres (each over at least a majorfraction of the electrode) which together define a point on a plot ofvoidage (x axis) versus loading ratio of the volume of lead to thevolume of conductive fibres (y axis) that falls within an area definedby one line on said plot from an x axis voidage value of about 98% witha slope of about −1/0.02 and the another line on said plot an x axisvoidage value of about 70% with a slope of about −1/0.3.

In some embodiments the voidage and mass loading ratio of lead to themass of conductive fibres when converted to volume ratio together definea point on said plot that falls within an area defined by one line froman x axis voidage value of about 97% with a slope of about −1/0.03 andanother line from an x axis voidage value of about 80% with a slope ofabout −1/0.2, or an area defined by one line from an x axis voidagevalue of 96% with a slope of −1/0.04 and another line from an x axisvoidage value of 85% with a slope of about −1/0.15.

In broad terms in another aspect the invention comprises a lead-acidbattery or cell including at least one (non-composite or compositeelectrode comprising as a current collector a carbon fibre materialhaving a carbon fibre volume fraction of less than 40%, and a loadingratio of the volume of lead (in whatever form) to the volume of carbonfibres greater than 0.5 (each over at least a major fraction of theelectrode and more preferably over substantially all of the electrode).

In some embodiments the carbon fibre volume fraction of less than 30%,and mass loading ratio of lead to carbon fibres converted to volumeratio is greater than 0.7, or the carbon fibre volume fraction is lessthan 20% and mass loading ratio of lead to carbon fibres converted tovolume ratio is greater than 1:1.

In broad terms in another aspect the invention comprises a lead-acidbattery or cell including at least one (composite) electrode comprisingas a current collector a conductive fibrous material, and comprising ametal grid, the electrode also comprising a current generatingelectrolyte active mass at least 20% of which is in the conductivefibrous material.

In some embodiments at least 40%, 50%, 80%, or not more than 80% of theactive mass is in the conductive fibrous material. Thus less than 80%,60%, 50%, or 20% of the active mass may be dispersed in the metal grid.

In some embodiments conductive fibrous material comprises a carbon fibrematerial and the metal grid comprises a lead grid.

In some embodiments the conductive fibrous material is present asmultiple layers at least one on either side of the metal grid.Alternatively the conductive fibrous material is present as a singlelayer on one side of the metal grid.

The metal grid may have a similar superficial surface area or be ofsimilar height and width dimensions particularly in a major plane, tothe conductive fibrous material element(s) but in alternativeembodiments the metal grid may have smaller dimensions for example ofsmaller height and width dimensions, and may comprise for example anarrower lead strip between two larger carbon fibre layers on eitherside thereof.

The carbon fibre layer(s) are conductively connected to the metal gridso that the grid receives current from the carbon fibre layer(s) andconnects the electrode externally thereof.

The conductive fibrous material may be a woven material (comprisingintersecting warp and weft fibres), a knitted material, or a non-wovenmaterial such as a felt material. The positive electrode or electrodes,the negative electrode or electrodes, or both, may be formed of one ormore layers of the conductive fibrous material. Preferably theconductive fibrous material density is also lighter than that of lead.The current collector material may comprise a carbon fibre material suchas a woven or knitted or felted or non-woven carbon fibre fabric. Carbonfibre current collector material may be heat treated to sufficienttemperature to increase its electrical conductivity. The thermaltreatment may be by electric arc discharge. Typically the conductivefibrous material has length and width dimensions in a major plane of thematerial and depth perpendicular to said major plane of the material.The current collector fibrous material may have an average depth of thematerial of at least 0.2 mm or at least 1 mm and/or less than 5 mm or 3mm or 2 mm. The current collector may comprise multiple layers of theconductive fibrous material. The current collector material has bulkresistivity less than 10 Ωmm and preferably less than 1 Ωmm or 0.1 Ωmm.

In broad terms in another aspect the invention comprises a lead-acidbattery or cell including at least one electrode comprising as a currentcollector a conductive fibrous material, and comprising a metal grid,the electrode also comprising a current generating electrolyte activemass, the conductive fibrous material having a bulk resistivity of lessthan 10 Ωmm.

In at least some embodiments, cells and/or batteries comprising anelectrode construction of the invention may have both improved orrelatively high DCA and CCA, and/or may maintain DCA or a higher rate ofDCA with an increasing number of charge-discharge cycles, and thus maybe particularly suitable for use in hybrid vehicles. Cells and/orbatteries of the same or other embodiments of the invention may also oralternatively have reduced water consumption and/or improved orrelatively high VED and/or improved battery life.

The term “comprising” as used in this specification means “consisting atleast in part of”. When interpreting each statement in thisspecification that includes the term “comprising”, features other thanthat or those prefaced by the term may also be present. Related termssuch as “comprise” and “comprises” are to be interpreted in the samemanner.

BRIEF DESCRIPTION OF THE FIGURES

The invention is further described with reference to the accompanyingfigures by way of example wherein:

FIG. 1 is a plot of ratio of active material to carbon (volumetricratio) versus voidage, for various negative electrodes used in a leadacid cell, all made up from active material loaded into a carbon matrix,

FIG. 2 is a plot of areas of ratio of active material to carbon(volumetric ratio) versus voidage, that also includes the variouselectrodes in FIG. 1,

FIG. 3a schematically shows a carbon fibre electrode with a metal lugfor external connection of the electrode formed on the carbon fibrematerial by pressure die casting, FIG. 3b shows a different shaped lugwith a tab addition, and FIG. 3c shows a cross-section of multiplelayers of carbon fibre material with a lug,

FIG. 4 schematically shows an electrode of an embodiment of theinvention from one side with a metal wire or tape attached to one sideas a macro-scale current collector,

FIG. 5 is a schematic cross-section through an electrode of anembodiment of the invention with a metal wire or tape attached to oneside as a macro-scale current collector,

FIG. 6 is a schematic cross-section through an electrode composed of twosections of electrode material of an embodiment of the invention with ametal wire or tape embedded or sandwiched between as a macro-scalecurrent collector,

FIG. 7 is a schematic cross-section view of illustrating felt splittingfor forming carbon fibre electrode material of some embodiments of theinvention,

FIG. 8 schematically illustrates one form of reactor for the continuousor semi-continuous activation of a carbon fibre material for use as acurrent collector material according to the invention,

FIG. 9 is a close up schematic view of the electrodes and the materialpath between the electrodes of the reactor of FIG. 8,

FIG. 10 shows the Axion DCA test algorithm referred to in the subsequentdescription of experimental work,

FIG. 11 shows the High Rate DCA performance of two composite electrodesN359 and 371 referred to in the subsequent description of experimentalwork,

FIG. 12 shows the CCA performance of electrode N439 referred to in thesubsequent description of experimental work, as tested using SAE J537 ata high rate of 310 mA/square cm of electrode surface area facing anotherelectrode,

FIG. 13 shows the current versus charging overpotential (Tafel Line) ofelectrode 411 referred to in the subsequent description of experimentalwork, as compared to a traditional electrode, demonstrating similarwater consumption properties,

FIG. 14 shows the current versus charging overpotential (Tafel Line) ofelectrode 305 referred to in the subsequent description of experimentalwork, but is shows less desirable water consumption properties than atraditional electrode,

FIG. 15 shows the High Rate DCA performance of electrode 409, a 60 mmlong electrode with a wire current collector, referred to in thesubsequent description of experimental work, which demonstrates good DCAperformance compared to a traditional electrode,

FIG. 16 shows the High Rate DCA performance of electrode 356 while 60 mmlong, with no wire current collector, referred to in the subsequentdescription of experimental work, which has DCA performance less than anelectrode with a wire current collector, but still better than atraditional electrode,

FIG. 17 shows the High Rate DCA performance for electrode 356 referredto in the subsequent description of experimental work, after the initial35,000 cycles (shown in FIG. 16) and reduced in length to 30 mm, andthen tested at the same charging current density as before, and showsexceptional DCA performance, and

FIG. 18 shows the DCA performance of electrode 410 when using the AxionDCA test, as compared to the typical DCA performance of a traditionallead acid Battery.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIG. 1 which is a chart of ratio of active material tocarbon (volumetric ratio) versus voidage, in one embodiment a lead-acidbattery or cell according to the invention includes at least oneelectrode comprising as a current collector a conductive fibrousmaterial comprising voidage (being the fractional volume occupied by thepores between the lead and conductive fibres) when fully charged of atleast about 0.3, and a mass loading ratio of lead (in whatever form) tothe mass of conductive fibres, when converted to volume ratio in therange about 0.7:1 or about 1:1 to about 15:1 or about 10:1. (andassuming full conversion of all active material to Pb when fullycharged). In some embodiments the voidage is between about 0.3 and 0.9,between about 0.3 and about 0.85, between about 0.3 and about 0.80,between about 0.5 and about 0.98, between about 0.7 and 0.95, betweenabout 0.5 and 0.98, or between about 0.8 and about 0.95, and the volumeloading ratio of the active material when converted to Pb to conductivefibres is between about 0.7:1 or about 1:1 and about 7:1, between about1.5:1 and about 5:1, or between about 2:1 and about 3:1.

The ratio of active material volume to carbon volume refers to thevolume of the Pb-containing active material in the conductive fibrousmatrix. Voidage refers to the void volume among the particles of activematerial and the conductive fibrous matrix, divided by the total volume.The solids volume ratio versus the voidage for a number of differentelectrodes described in the subsequent experimental examples is shown inFIG. 1. FIG. 1 allows for different matrix voidages, variation of theextent of filling this matrix voidage with solid active material forexample at pasting, and variation in state of charge. Each line is drawnbetween the volume ratio and voidage for two extreme forms of the activematerial contained in a given carbon matrix. For most electrochemicalcycling these two forms are Pb and PbSO₄. Electrodes made with aspecific carbon matrix occupy a single line on the chart, and passthrough the point of matrix voidage with no active material. The extentof active material loading (and the form it is in e.g. PbSO4, or Pb)determines which point on the (straight) line the electrode is(currently) represented by, taking account of the different densities ofthe different forms, and how much of each is present. For example, ifthe matrix is initially loaded with PbSO₄, and then fully charged to Pb,this formation is represented by travelling along a section of the line,“fully discharged” to “fully charged”. If the matrix is initially loadedwith PbO and then fully charged to convert this to Pb, then a differentline is drawn to represent the path from PbO to Pb. However after thisfirst conversion to Pb, the path followed in any subsequent cycling willfollow the line between Pb and PbSO₄. Thus discharge/charge from thisfull charge point on will be represented by paths along the same line aswhen initially loaded with PbSO₄. Only when it is fully charged (i.e.,at 100% Pb) will the electrode using PbO as the precursor be representedon the more useful PbSO4/Pb line and thereafter i.e. during furthercycles, the electrode path will be on that line. The lines labelled 349,363, and 441 in FIG. 1 are for electrodes the construction of which isdescribed in the subsequent experimental examples. The lowermost pointsof each line represents the conditions where all the loaded activematerial has been converted to Pb.

The voidage within the electrodes of a lead-acid cell or battery isimportant for both containing one of the active materials—the acid—andfor allowing ions access to the surface that supplies or acceptselectrons. We express this volume as the fraction of the total volume(‘voidage’) of the part of the electrode containing the electrolyte. Theratio of volume of lead to volume of conductive fibre such as carbonfibre refers to the balance between the matter (Pb) potentially capableof yielding charge or accepting it, and the matter of conductive fibresuch as carbon fibre providing a conduit for the electrons andoptionally also a catalytic surface for the electrochemical reactions.This ratio may be expressed as a volume ratio. Both volume and massratios can be calculated for the fully charged state (where only Pbexists) and fully discharged state (only PbSO₄). In normal cyclingcharge and discharge, the discharge finishes before reacting 100% of thePbSO₄. Any given electrode can be characterised by two parameters: 1.the matrix voidage before loading with active material (or moreconveniently the matrix volume fraction which is 1 minus this voidage),and 2. the volume ratio of the active material and carbon matrix whenthe active material has been fully converted to lead. A furtherparameter can be represented on the chart. The utilization of lead toprovide charge is the fraction of the total possible path traveled fromPb to PbSO₄ that the electrode is capable of during discharge.

The volume ratio that is of importance for reaction rates is the voidageof the electrode material and lead-containing particles. This voidage isneeded to allow the ions of acid and Pb++ to diffuse to and from thereacting surface.

FIG. 2 is similar to FIG. 1 but also shows lines characterised bycertain carbon matrix volume fractions which define areas of ratio ofactive material to carbon (volumetric ratio) versus voidage. Line a1labelled C=2% extends from an x axis voidage value of 98% with a slopeof −1/0.02 and line a2 labelled C=30% extends from an x axis voidagevalue of 70% with a slope of −1/0.3. Electrodes which when fullycharged, have a voidage and a mass loading ratio of lead to the mass ofconductive fibres when converted to volume ratio which define a point inthe area between lines a1 and a2 are electrodes of embodiments of theinvention.

Line b1 labelled C=3% extends from an x axis voidage value of 97% with aslope of −1/0.03 and line b2 labelled C=20% extends from an x axisvoidage value of 80% with a slope of −1/0.2. Electrodes which when fullycharged, have a voidage and a mass loading ratio of lead to the mass ofconductive fibres when converted to volume ratio which define a point inthe area between lines a1 and a2 are electrodes of preferred embodimentsof the invention.

Line c1 labelled C=4% extends from an x axis voidage value of 96% with aslope of −1/0.04 and line c2 labelled C=15% extends from an x axisvoidage value of 85% with a slope of −1/0.15. Electrodes which whenfully charged, have a voidage and a mass loading ratio of lead to themass of conductive fibres when converted to volume ratio which define apoint in the area between lines a1 and a2 are electrodes of morepreferred embodiments of the invention. In particular such electrodesmay be used for forming cells and/or batteries with both improved orrelatively high DCA and CCA, and may also have low water consumption,which are particularly suitable for use in hybrid vehicles.

The slope of lines a1 & a2, b1 & b2, and c1 & c2 is described by theformula relating voidage and the ratio of volume of lead to volume ofconductive fibre:

$R = {\frac{1 - \phi_{c}}{\phi_{c}} - \frac{ɛ}{\phi_{c}}}$where ε is voidage, R is the ratio of volume of lead to volume ofconductive fibre, and φ_(c) is the volume fraction of the carbon matrix.The lowest point on this line is that describing the fully leadcondition, which we can label as R_(Pb), ε_(Pb).

The cycling performance may depend on maintaining a suitably smallparticle size for the Pb and PbSO₄ particles after many cycles. Thissmall particle size gives a sufficient surface area for sufficientdissolution of PbSO₄ or Pb into Pb++ to give the rates and currentsrequired, when the particles are close to a carbon fibre surface, whichcatalyses the current creation reactions. The size of the particlesafter many cycles may be closely related to the size of the interfibrespacing between the conductive fibres, so that the particles fit betweenthem. Thus with smaller diameter conductive fibres at the same totalvolume fibre fraction the gaps between these will be proportionatelysmaller and also the active particles will be proportionately smaller.Thus higher surface areas and higher rates may be achieved with smallerfibres.

In relation to the ratio of particle size to diameter of the conductivefibre, as the particle size changes extensively during electrodecycling, the final particle size is somewhat independent of the startingsize. However the starting size should be chosen small enough to fiteasily between the fibres, such as less than around 10 microns for 7 or8 micron diameter fibres for example. It is expected that the erodingaction of each carbon fibre on the surrounding PbSO₄ particles duringcharging keeps these from growing larger over many cycles. Thus‘sulphation’ may be reduced or avoided and long cycle life obtained.

A stated the conductive fibrous material may be a woven material(comprising intersecting warp and weft fibres), a knitted material, or anon-woven material such as a felt material. The current collectormaterial preferably has bulk resistivity less than 10 Ωmm and preferablyless than 1 Ωmm or 0.1 Ωmm. The material may comprise a carbon fibrematerial such as a woven or knitted or non-woven or felted carbon fibrefabric. Non-woven materials with random fibre entanglement andintersections may be advantageous over woven materials with regularintersections of warp and weft fibres at right angles.

Suitable carbon fibre material may comprise or be derived from rayon,polyacrylonitrile, phenol resin, or pitch materials.

Typically the conductive fibrous material has length and widthdimensions in a major plane of the material and an average thicknessperpendicular to said major plane of the material, which may be forexample about 0.2 mm or about 1 mm and/or less than 5 mm or less than 3mm or less than 2 mm.

In at least some embodiments the conductive fibrous material also has anaverage spacing between conductive fibres in the range about 0.5 toabout 10 times or about 1 and about 5 times the average fibre diameter,or less than about 20 microns, or less than about 10 microns, and anaverage conductive fibre diameter of less than about 10 microns.

Felt or other non-woven planar electrode material may be produced tovery low thickness such as for example 2.5 mm or less thickness bydividing thicker material in plane. That is, the material may be cut inits plane one or more times to divide a thicker non-woven material intomultiple sheets of similar length and width but reduces thickness to thestarting sheet. This is schematically illustrated in FIG. 7 which showsfine cutting blade 60 which passes continuously around and is driven bydrive rollers 61 and 62, in plane slicing carbon felt sheet 63 on bed 64to form two carbon felt sheets of the same length and width but halfthickness. Each resulting carbon sheet may be further in plane divided.

Woven carbon fibre material may be woven from carbon fibre tows whichhave been ‘stretch broken’ ie a tow (bundle) of a larger number ofcontinuous carbon fibre filaments is stretched after manufacture tobreak individual continuous filaments into shorter filaments andseparate lengthwise the ends of filaments at each break, which has theeffect of reducing the filament count of the carbon fibre tow. Theresulting reduced filament count tow is twisted (like a rope) tomaintain tow integrity. For example a tow of 50,000 continuous filamentsmay be stretch broken to produce a much longer tow composed of 600shorter individual filaments which is then twisted, for example.

In at least some embodiments the conductive fibrous material comprisesfilaments of average length in the range 3 to 50 mm.

The negative electrode or electrodes, the positive electrode orelectrodes, or both, of a cell or battery may be formed as above.

In preferred embodiments the conductive current collecting materialfibres are inherently conductive. In preferred embodiments the electrodefibres are carbon fibres. However the carbon fibre material may in someembodiments be treated to increase conductivity. In other embodimentsthe electrode fibres may be a less conductive microscale material, thefibres of which are coated with a conductive or more conductive coating.In some embodiments the fibres of the current collector material may becoated with Pb or a Pb-based material. For example the negativeelectrode or electrodes may be coated with Pb and the positiveelectrode(s) coated with Pb and then thereon PbO₂.

Preferably the current collector material and the fibres thereof areflexible, which will assist in accommodating volume changes of theactive material attached to the current collector material duringbattery cycling, and the microscale fibres may also reinforce the activematerial, both properties assisting to reduce breaking off (“shedding”)of active material from the electrode in use.

In some embodiments the conductive fibrous material comprises the solecurrent collector of the or each electrode.

Alternatively the or each electrode may comprise a metal grid also as acurrent collector in addition to the conductive fibrous material ofcarbon fibre. In preferred embodiments conductive fibrous materialcomprises a carbon fibre material and the metal grid comprises a leadgrid. The carbon fibre layer(s) are conductively connected to the metalgrid so that the grid receives current from the carbon fibre layer(s)and connects the electrode externally thereof.

The negative or positive or both electrodes of each cell may comprise ametal grid.

Where the electrode comprises a metal grid preferably at least 20% ofthe current generating active mass is dispersed through the conductivefibrous material. In preferred embodiments at least 40%, 50%, 80%, ormore than 80% of the active mass is dispersed in the conductive fibrousmaterial. Thus less than 80%, 60%, 50%, or 20% of the active mass may bedispersed in the metal grid (specifically, within its apertures).

In some embodiments at least 20% but not more than 40% of the activemass is dispersed through the conductive fibrous material.

In preferred embodiments the conductive fibrous material is present asmultiple layers one or more on either side of the metal grid.Alternatively the conductive fibrous material is present as a singlelayer on one side of the metal grid.

The metal grid may have a similar superficial surface area or be ofsimilar height and width dimensions particularly in a major plane, tothe conductive fibrous material element(s) but in alternativeembodiments the metal grid may have smaller dimensions for example ofsmaller height and width dimensions, and may comprise for example anarrower lead strip between two larger carbon fibre layers on eitherside thereof.

Typically during battery or cell construction the microscale currentcollector material is impregnated under pressure with a paste, which ina preferred form comprises a mixture of Pb and PbO particles of Pb andPbO and dilute sulfuric acid. Alternatively the paste may comprise leadsulphate (PbSO₄) particles and dilute sulphuric acid. In someembodiments the paste at impregnation into the electrode comprisesdilute sulphuric acid comprising between greater than 0% and about 5%,or between 0.25% and about 3%, or between 0% and about 2%, or between0.5 and 2.5% by weight of the paste of sulphuric acid. The Pb-basedparticles may comprise milled or chemically formed particles which mayhave a mean size of 10 microns or less, small enough to fit easily intospaces between the fibres.

The paste may optionally also contain other additives such as carbonblack, barium sulphate, and/or an expander such as a lignosulphonate.Barium sulfate acts as a seed crystal for lead sulphate crystallisation,encouraging the lead to lead sulfate reaction. An expander helpsprevents agglomeration of sulphate particles at the negative plate, forexample forming a solid mass of lead sulfate during discharge.

For example an expander may comprise between about 0.05% to about 0.25%or about 0.09 to 0.2% or about 0.09 to 0.17% by weight of the paste atimpregnation. It has been found that the inclusion of an expandercompound in the paste may have a beneficial effect on CCA performancebut a negative effect on DCA performance. Conventionally an expander ata concentration of around 0.2% or more is added to the paste. It hasbeen found that at an expander concentration of between about 0.09% toabout 0.15% by weight of the paste at impregnation both good DCA and CCAperformance can be achieved.

The paste may also comprise Ag, Bi, Zn, or a compound of any thereof asan anti-gassing agent.

The paste may have relatively low viscosity for example flow rather thanbe self supporting on a horizontal surface under gravity, atimpregnation into the electrode material. Preferably the paste has acreamy consistency. It has been found that this is achieved where thepaste at impregnation into the electrode comprises (greater than 0 but)less than 5% by weight of dilute sulphuric acid.

To aid impregnation of the electrode material by the paste a lowfrequency vibration for example at less than 2 kHz or less than 1 kHz orin the range 50 to 500 Hz may be applied to the paste or the electrodematerial or both. It has also been found useful when mixing the Pb-basedparticles, sulphuric acid, and water to form the paste, to aid mixing byvibration of the paste during mixing.

During initial cell formation (first charge and discharge cycle duringwhich active particle linkages form) after cell or battery construction,cell formation occurs first by building the conducting framework, takingup most of the Pb in the negative active material, building normallyover lengths of several millimetres (connecting strings of perhaps athousand or more micron sized particles end to end). This stage alsoproduces small PbSO₄ particles. Second, these smaller particles attachto this conductive framework to provide and receive current. Inaccordance with the invention the Pb grid is replaced or supplemented bya microscale fibrous current collector and the paste comprises PbSO₄ orPbO or Pb particles (or other particles of Pb compounds), requiringduring formation substantially only attaching the Pb from these Pbcontaining particles to the nearest fibres in the microscale conductivecurrent collector material. It may be advantageous that during formationthe charging current is pulsed periodically.

The fibrous current collector material may be supported mechanically anda supporting mechanical frame may also provide electrical connection ofeach electrode to the cell or battery terminals (external electrodeconnection). For example one or more square or rectangular adjacentlayers of the current collector material may be supported to form aplanar battery plate by a peripheral metal frame on all sides or betweenopposite metal frame elements on two opposite sides. Alternatively forexample concentric cylindrical positive and negative plates of each cellmay comprise cylindrical sections of the microscale current collectorsupported at either cylindrical end by circular metal frames. Generallyall forms of external connector are referred to herein as a ‘lug’.

FIG. 3a schematically shows woven carbon fibre electrode 50 with a metallug 51 for external connection of the electrode formed on the carbonfibre material by pressure die casting, FIG. 3b shows a different shapedlug with a tab addition 53, and FIG. 3c shows a cross-section ofmultiple layers of carbon fibre material with a lug. The lug is formedof metal such as Pb or a Pb alloy (herein both referred to inclusivelyas Pb) but may be formed of another material which electrically connectspreferably by penetration into and/or between the fibrous material.Preferably the lug extends substantially fully along an edge of theelectrode. For example if the electrode has a square or rectangularshape the lug extends substantially the full length of one edge of theelectrode. Preferably the lug is substantially no thicker than theelectrode material itself.

In some embodiments substantially all or at least a majority offilaments/fibres of the electrode material extend continuously acrossthe electrode between or to a metal frame or frame elements to whichboth ends or at least one end of the fibres is/are electricallyconnected. A woven fabric of continuous fibres may be optimal.

The electrical connection between the carbon fibres and the lug orconductive frame should be a minimum resistance join and in a preferredform each fibre end is surrounded with a molten metal which physicallyfixes and electrically connects the fibre end to the metal frame, duringbattery or cell construction. The metal frame or frame elements maythemselves be formed by cooling molten metal strips along one or moreedges of the electrode material to surround and embed the fibre ends.Optionally the fibres or fabric can continue beyond one or more frameelements at one or more edges to form another adjacent electrode orelectrode section. Preferably substantially all or at least a majorityof electrode fibres in one direction or in plane axis of the materialare electrically connected to a metal frame element not more than 100 mmto 10 mm away from where the fibre starts in the active material or atboth opposite edges of the material. This distance or the size or areaof each current collector material section is mainly determined by thebulk resistivity of the current collector material in the mostconducting direction. If only one edge of the fabric is electricallyconnected to a metal frame element, preferably this most conductingdirection in the fabric is aligned perpendicular to the connected edgeto minimize the overall resistance. To allow highest current density inan electrode without significant capacity loss, the length of the fabricfrom the connected edge may be up to about 50 to 100 mm. A metal framemay alternatively comprise a metal sheet with apertures, on one or bothsides of the material, leaving the apertures or windows with solelycarbon fibres carrying the current and collecting from the activematerial that they carry. For example an electrode frame of height 200mm, may comprise two windows of height each 100 mm, with a conductingweb left around the edge so that the farthest distance from any crossbaris 50 mm. For each of these window regions, carbon fabric can be spreadand attached within the metal cross-bars and within the edges.

FIG. 4 schematically shows an electrode 55 from one side with a metallug 56 along one edge similar to FIG. 3. In this embodiment theelectrode on one or both sides of a carbon fibre material comprises ametal wire or tape 57 electrically conductively attached to theelectrode material 55 and to the lug 56, to provide an additionalmacro-scale current collecting pathway from the carbon fibre to themetal lug 56, in addition to the micro-scale pathways through the carbonfibre material itself of the electrode. The metal wire or tape may beattached to the electrode material for example by stitching or sewingwith a thread that will not dissolve in the electrolyte, or other inertPb acid battery binding material that will hold the current collector inplace, such as a resin, cement or potting mix. The metal wire or tapemay be pressed into the electrode material during manufacture.Alternatively the wire or tape or similar may be soldered to or printedon the carbon fibre electrode material. The metal wire or tape(s) may bearranged in a sinuous shape on one or both sides of the carbon fibrematerial as shown, extending continuously between the lug 56 at one edgeof the electrode, at which edge the wire or tape is conductivelyconnected to the lug 56 by being embedded in the lug, and at or towardsanother spaced edge of the electrode as shown. Alternatively the wire ortape may extend between metal lugs along opposite edges of the electrodeor a frame around the electrode. Alternatively again separate lengths ofthe wire or tape may extend from the lug at one edge to or towardsanother edge of the electrode, or alternatively again the wire or tapemacro-conductor as described may comprise a metal mesh attached on oneor both sides of the carbon fibre material.

FIG. 5 is a schematic cross-section through an electrode 55 with a metalwire or tape 56 attached to one side of the electrode material and FIG.6 is a schematic cross-section through an electrode composed of twolayers 55 a and 55 b of carbon fibre material with a metal wire or tape56 embedded or sandwiched between. The carbon fibres with metal wire ortape between may be compressed together during manufacture.

If formed from copper the wire or tape or mesh or similar including anyexposed ends thereof should be protected from oxidation within the cellby coating with lead or titanium or other metal inert in the Pb-acidenvironment, by for example hot dipping, extrusion, or electroplating.The ends of the wire or tape or mesh may terminate and be embedded inthe lug or peripheral frame. It is important that when the currentcollector is on the outer surface of the electrode that acts as thenegative electrode the current collector is protected from anodicoxidation from the positive electrode.

Preferably the wire or tape runs up and down the length of the electrodewith equal spacing across the width of the electrode without any crossover points as shown in FIG. 3, to prevent local hotspots occurring orheat build up in particular areas, and an even current collection acrossthe electrode.

Preferably the volume of the wire or tape or mesh or similar macro-scalecurrent collecting system is less than about 15% of the volume of theelectrode (excluding the lug or surrounding metal frame or similar).

In some embodiments electrodes of the invention whether composite (alsoincorporating a metal grid) or non-composite (without a metal grid) havea thickness (transverse to a length and width or in plane dimensions ofthe electrode) many times such as 10, 20, 50, or 100 times less than theor any in plane dimension of the electrode. The electrode thickness maybe less than 5 or less than 3 mm for example. Each of the in planelength and width dimensions of the electrode may be greater than 50 or100 mm for example. Such electrodes have a planar form with lowthickness. One form of composite electrode of the invention may comprisea metal grid of thickness about 3.5 mm mm or less such as about 0.5 mmmm thick, with a carbon fibre layer of thickness about 2 mm or less suchas about 0.3 mm thick on either side.

In preferred forms the electrode is substantially planar and has adimension from a metal lug for external connection along at least oneedge of the electrode less than 100 mm or less than 70 mm, or less than50 mm, or about 30 mm or less for example (with or without a macro-scalecurrent collector). Alternatively such a planar form may be formed intoa cylindrical electrode for example.

Carbon fibre material for use as the electrode current collectormaterial may be thermally treated. Thermal treatment may also increasethe thermal conductivity of the material, which should be sufficient toprevent local hot spots on the electrode in use. Carbon fibres aregenerally hydrocarbon-based and during manufacture heated to around1100° C. or more (“carbonised”). For use as current collector materialin batteries or cells of the invention, carbon fibre material may beheated further, generally in the range 2200 to 2800° C., to enlargeregions in the carbon that are already aromatic or graphitic, increasingelectrical conductivity. Thermal treatment to increase electrical and/orthermal conductivity may be in a resistively heated furnace for exampleor may be by electric arc discharge where in addition at least some or amajor fraction of non-graphitic carbon from the carbon fibres, and nomore than a minor fraction of graphitic carbon, may be evaporated off.

Carbon fibre current collector material may be heat treated tosufficient temperature to increase its electrical conductivity. Thethermal treatment may be by electric arc discharge. In certainembodiments carbon fibre material may be treated by arc discharge bymoving the carbon fibre material within a reaction chamber eitherthrough an electric arc in a gap between two electrodes or past anelectrode so that an electric arc exists between the electrode and thematerial at a temperature effective to activate the material. In FIG. 8,reference numeral 1 indicates a reactor chamber in which the dischargearc is created. Electrodes 2 and 3 project into the reactor chamber 1and are typically mounted by electrode-feeding mechanisms 4 as are knownin the art, so that the position of electrode 3, which maybe the anode,and electrode 2, which may be the cathode (the positions of the anodeand cathode may be reversed), may be adjusted to create the arc, and inoperation to maintain or if required adjust the arc. A cooling system 5consisting of copper tube coils wound around each electrodes throughwhich water is circulated may also be arranged to cool the electrode(s).Carbon fibre material 8 passes between electrodes 2 and 3 and throughthe arc during operation of the reactor, as shown. This is shown in moredetail in FIG. 9. The current should be sufficient to vaporisenon-graphitic carbon but not trigger the destructive localised arcattachment mode Operation between 10 A and 20 A is recommended. Thematerial may enter the reactor chamber through a slit 12 in the reactorchamber and leave through a similar exit slit 13 in the reactor chamberon the other side of the electrodes. A mechanism is provided to feed thematerial through the reactor chamber. For example during operation ofthe reactor the substrate may be unwound from a spool 9 driven by agearbox which is coupled to an electric motor with an appropriatecontrol system. During operation the interior of the reactor ispreferably at or slightly above atmospheric pressure, and the gas flowexiting the reactor through slit 13 is extracted via a fume hood orfilter or similar. An inert gas such as nitrogen, argon or helium forexample is flushed through the reaction chamber, for example byintroducing a controlled gas flow inside the reaction chamber 1 throughone of the openings 11 at the base of the reactor. The anode as well asthe spool which drives the tape are preferably earthed. Any take-upmechanism for collecting the substrate after it has passed through thereactor chamber is also preferably earthed, as is also the reactorshell. Referring to FIG. 9, it may be preferable for one electrode,which in the figure is the anode 3, to be positioned to impinge on thesubstrate 8 such that the substrate is tensioned against that electrodeas the substrate moves past it as schematically shown. Electric arcdischarge may vaporise a major fraction of non-graphitic carbon and nomore than a minor fraction of graphitic carbon of the carbon fibrematerial. The method may be carried out in the presence of an introducedmetal additive such as a Pb additive.

A microscale electrode in accordance with the invention with an internalpore surface area may provide capacitance sufficient to add to chargeacceptance over and above the electrochemical contribution. An electrodearea that is well wetted by and accessible to the acid electrolyte maycontribute more than an order of magnitude larger capacitance than thatgiven by the total surface area of a conventional active material in thenegative electrode of a lead-acid battery. It may have sufficientelectrolytic double-layer capacity to absorb or deliver several secondsof high current. Alternatively a battery of the invention may comprise aseparate high surface area electrode, which may comprise arc-treatedcarbon fibre material as described herein, in parallel to the or eachnegative or positive cell electrode, to add or increase capacitance.

Thermal treatment for example by electric arc discharge may increasepore surface area and increase capacitance. Also applying and thendrying an Pb(NO₃)₂ solution onto carbon fibre material before arctreatment may increase surface area development (apparently throughoxidation). Alternatively the material may be activated by physicalactivation such as by steam or carbon dioxide at temperatures around1000° C., or by chemical activation by for example alkali solutions.Activation typically creates pores of nanoscale and most typically up to50 nm in diameter, in the material, or on the surface of the material.Materials with extensive pores smaller than around 1 nm may not be goodelectronic conductors. Pores from 1 nm to around 10 nm may provide thesurface area required for significant capacity, but pores welldistributed above 10 nm are also needed to provide easy diffusionalaccess of ions for adequate electrolyte conductivity. Also required issufficient electrical conductivity within the solid.

In some embodiments carbon fibre material has carbon nanotubes (CNTs)attached thereto. The CNTs bearing material may be produced by electricarc discharge treatment of the carbon fibre material, or alternativelyby chemical vapour deposition at lower temperatures in the presence of acatalyst.

As stated, in preferred forms suitable for use in hybrid vehicles cellsand/or batteries comprising an electrode construction of the inventionmay have both improved or relatively high DCA and CCA (DCA measured bythe Axion test and CCA as measured in accordance with the SAE J357 CCAtest for example, and/or may maintain DCA or a higher rate of DCA withincreasing number of charge-discharge cycles, and may also have lowwater consumption, and may also have improved or relatively high VEDand/or improved battery life. Embodiments of cells or batteries of theinvention may maintain DCA at least 70% or 80% or 90% of starting DCA(when first fully charged) after 5000 or 10000 cycles for example.Embodiments of cells or batteries of the invention may retain an averageDCA of at least 0.6 or 0.7 or 0.8 A/Ah per charging phase at 10,000cycles using the Axion DCA Test. The capacity of a battery is measuredin Amp/hours, and utilisation is the actual battery capacity divided bythe theoretical maximum capacity, and embodiments of cells or batteriesof the invention may have increased utilisation such as a utilisation ofat least 55%, 60%, 70%, or 80% or over.

EXAMPLES

The following description of experimental work which is given by way ofexample further illustrates the invention. In some of the examples a DCAtesting is referred to and FIG. 10 shows the DCA test algorithm inaccordance with which a high rate dynamic charge acceptance test (DCAT)designed to simulate the demands a stop/start micro hybrid vehicle onits battery system was applied to each cell. The DCAT test profile is anaccelerated, destructive life time test on the battery which is held ata constant state of charge, which ensures the DCAT test is independentof the test system and calibration issues associated with that system,thus avoiding calibration issues normally associated with other lifetimetest protocols. The DCAT test employed followed the Axion DCAT testprofile on a Cadex C8000 test system, where the test profile consists ofthe following steps:

-   -   0.51 C discharge for 60 s    -   3.15 C pulse discharge for 1 s    -   10 s rest (at the end of which PDRV (Post discharge rest        voltage) is measured)    -   1.05 C dynamic charge period adjusted to hold PDRV at a given        set point    -   10 s rest.

This described cycle profile is iterated to a cycle count of 30,000which translates to a typical 6 week period, although this period isdependent on battery performance. Every 5000 cycles, a full chargefollowed by a deep discharge measured the electrode capacity. To passthis test, the cell needs to be able to cycle through the DCAT test atleast 30,000 times while retaining the capacity at least 2 Ah. 30,000cycles is representative of a battery lifetime in a micro hybrid ofapprox. 3 years.:

Example 1—Composite Electrode of Carbon Fibre Paper with Pb Grid—N371

Method: An electrode was constructed from carbon fibrous paper carbonmat (Z-Mat produced by Zoltek) of thickness of 3 mm, ˜6% carbon fractionin volume, specific weight˜312 g/m², and fibre length of 25 mm. Twopieces were cut to dimensions 44 mm*70 mm and then split into thinnerlayers to produce individual layers of average thickness of 0.26 mm. Theelectrode was constructed by placing one of these carbon fibrous layerson each of the two surfaces of a lead grid.

Paste was prepared with 23.2 g of leady oxide (leady oxide batchpurchased from Exide in 2009), 4.0 g of diluted sulphuric acid, 2.7 g ofVanisperse A (expander) aqueous solution with enough Vanisperse A toachieve 0.10 wt % in the prepared paste and 0.187 g of barium sulphate.The paste was mixed in an ultrasound bath for 2 minutes (53 kHzfrequency, at 23° C. tank temperature). One of the fibrous layers wasplaced on a flat plate and the lead grid was then placed on top of thefibrous layer. The Pb grid had thickness 2.02 mm, length 66.3 mm, width44.2 mm, and open volume fraction ˜81.6%. Paste was spread on the leadgrid surface until a smooth distribution of paste on the surface wasobtained where all grid pockets were filled with the paste. Sufficientexcess paste to partly fill a fibrous layer was then spread over thepasted grid surface and a second carbon fibrous layer then placed ontop. Further paste was spread on the top surface to get a smooth andeven surface. Excess paste was removed from both faces and the sideedges of the electrode. The total thickness of the pasted electrode wasapproximately 2.60 mm.

The total amount of wet mass loaded in to the composite electrode was24. 41 g where the achieved capacity (low current discharging) was 2.695Ah (i.e. 60% of the theoretical capacity). Assuming the pastepenetrated/dispersed into the grid and the fibrous layers evenly, 19.8%of NAM dispersed into the fibrous layers of the electrode and theremainder was in the lead grid. At the fully charged state of theelectrode, the average active mass Pb to carbon volume ratio is 10.03.The average spacing between carbon fibres was about 23 microns.Subsequently the electrode was air-dried for 24 hours at ambienttemperature (18° C.-24° C.) and then the pasted electrode was assembledin a cell containing electrolyte of 1.15 sg H₂SO₄ with one (40% SOC)positive electrode on each side. The cell was left soaking for 24 hoursat ambient temperature (18° C.-24° C.) and cell standard formation wascarried out.

Test method(s) and results: The electrolyte was replaced with 1.28 sgH₂SO₄ and stabilised under four cycles of low current discharging (0.06C) prior to being sent to the high rate DCA. The high rate dynamiccharge acceptance test (HR-DCAT) was carried out on the cells inaccordance with the test as described above and as shown in FIG. 11. Theresults are show in table 1 below.

Example 2—Composite Electrode of Arc Treated Carbon Fibre Woven Fabricwith Pb Grid—N359

Method: An electrode was constructed of woven carbon fibre fabric PAN[polyacrylonitrite] based woven carbon fibre tape (manufactured byTaiCarbon, Taiwan). The fabric was treated in an electric arc generallyas previously described with reference to FIGS. 8 and 9. Thisarc-treated fabric had 136 g/m² specific weight, was 0.38 mm thick, andhad ˜20% carbon volume fraction. Two pieces of the arc-treated fabricwere cut into the size of 44 mm*70 mm. One piece of arc-treated fabricwas placed on an ultrasound plate and the lead grid placed on top ofthat. The Pb grid had dimensions thickness 1.94 mm, length 66.7 mm,width 44.4 mm, and open volume fraction ˜81.1%. Paste was prepared andthe electrode was pasted and constructed using a second layer of thecarbon fibre fabric, all as described in example 1. The total thicknessof the pasted electrode was approximately 3.6 mm.

The total amount of wet mass loaded into the composite electrode was 28g where the achieved capacity (low current discharging) was 2.99 Ah(i.e. 60% of the theoretical capacity). Assuming the pastepenetrated/dispersed into the available void volume of the grid and thefibrous layers evenly, 28.1% of NAM dispersed into the carbon fibrouslayers of the composite electrode and the remainder was in the leadgrid. At the fully charged state of the electrode, the average activemass Pb to carbon volume ratio is 3.20. The average spacing betweencarbon fibres was about 15 microns.

Subsequently the electrode was air-dried, assembled in a cell, the cellwas left soaking, and then formation charging and stabilisation wascarried out in the cell, all as described in example 1.

Test method(s) and results: The electrolyte was replaced with 1.28 sgH₂SO₄ and stabilised under four cycles of low current discharging (0.06C) prior to being sent to the high rate DCA. The high rate dynamiccharge acceptance test (HR-DCAT) was carried out on the cells inaccordance with the test as described above and as shown in FIG. 11. Theresults are show in table 1 below.

TABLE 1 compares the results of the DCAT testing of the electrodes setout in examples 1 and 2 above. Mass of % of Electrode Electrode paste inNAM in DCAT Electrode material thickness electrode CF results N371Carbon 2.62 mm 24.41 gm 19.8% Steep fibre total (Pb decline paper grid2.02 in with mm, CF performance approx. (0.52 mm from early in 6%comprised the test. carbon of 2 layers) vol fraction Pb Grid- IndustrialN359 Arc  2.7 mm  27.1 g  28.1% Cell still treated total operating woven(1.94 mm above 2 Ah PAN Pb grid, CF at 35,000 woven 0.76 mm cyclescarbon comprised fibre tape of 2 layers) with approx. 20% carbon volfraction

Example 3—Non-Composite Electrode of Arc Treated Carbon Felt, ActiveMass/Carbon Volume Ratio ˜2.698-N363—see FIGS. 1 and 2

Method: An electrode was constructed of carbon fibrous layers ofarc-treated carbon felt Sigracell KFD2.5 EA manufactured by SGL CarbonCompany, Germany). The felt was treated in an electric arc generally aspreviously described with reference to FIGS. 8 and 9. The felt beforearc-treatment had a specific weight of 248 g/m², thickness of 2.5 mm,and carbon volume fraction ˜7%. The material post arc-treatment had 217g/m² specific weight, was 2.4 mm thick, and had ˜6% carbon volumefraction.

The method of pasting for the single layer of felt is different to thatdescribed above for layers of woven fabric. Paste was prepared startingwith 19.5 g of leady oxide (leady oxide batch purchased from Exide in2009) to the same composition as set out in examples 1 and 2 above andfollowed the same mixing procedure in the ultrasound bath under sameconditions. The carbon felt piece was placed on the plate which used forpasting. Then the above prepared paste was spread on the felt layeruntil a smooth distribution of paste on the surface was obtained. Thefelt piece was then placed on the ultra-sound vibration plate so thatthe un-pasted surface faced up and paste was distributed on this surfaceusing a flexible plastic spatula. Ultrasound vibration was on for ˜50sec during pasting. (Ultra-sound vibrating plate manufactured by SkymenCleaning Equipment Shenzhen Co. Ltd was used, current rating on the USplate used was 1.75 A, the electrode was placed covering one transducerpoint on the plate). The pasted electrode was turned over couple oftimes while the ultra-sound was in operation until a smooth distributionof paste on surface appeared to have been achieved, but where themajority of the paste had penetrated into the felt.

The total amount of wet mass loaded in to the composite electrode was19.5 g where the achieved capacity (low current discharging) was 2.4 Ah(i.e. 66% of the theoretical capacity).

The pasted electrode active area (pasted) dimensions were length 67.4mm, width 45.6 mm, and thickness 2.44 mm. The achieved lead loading pervolume (pasted density of the electrode based on the mass loaded on tothe electrode) was 1.91 g/cm³. At the fully charged state of theelectrode, active mass Pb to carbon volume ratio was 2.698. The averagespacing between carbon fibres was about 36 microns.

Subsequently the electrode was air-dried, assembled in a cell, the cellwas left soaking, and then formation charging was carried out in thecell, all as described in example 1.

Test method(s) and results: The electrode was tested as described inexamples 1 and 2 with the results set out in Table 2.

Example 4—Non-Composite Electrode of Arc Treated Carbon Felt, ActiveMass/Carbon Volume Ratio ˜4.52-N439—see FIG. 12

Method: An electrode was constructed of carbon fibrous layers ofarc-treated carbon felt (Sigracell KFD2.5 EA) manufactured by SGL CarbonCompany, Germany). The felt was treated in an electric arc generally aspreviously described with reference to FIGS. 8 and 9. The felt beforearc-treatment had a specific weight of 248 g/m², thickness of 2.6 mm,and carbon volume fraction ˜6%. The material post arc-treatment had 197g/m² specific weight, was 2.33 mm thick, and had ˜6% carbon volumefraction.

Lead coated Cu wires-0.38 mm in diameter were used as an additionalcurrent collector for the above electrode. These were laid on the feltsurface manually along the length of the felt in a zig-zag manner withthe vertical strips evenly spaced along the width, prior to injectingthe lug. The lug was injected onto the felt so that the top of each zagof the Cu wire was immersed in the lug and attached to the lug.

Method of Pasting:

Paste was prepared with 23 g of leady oxide (leady oxide batch purchasedfrom Exide in 2009), 1.5 g of diluted sulphuric acid, 0.023 g ofVanisperse A (expander) to achieve 0.1% expander in the paste and 0.184g of barium sulphate. The same mixing procedure was followed for pastepreparation and pasting as explained in previous examples of N363 andN364. Ultrasound vibration was on for ˜1.30 min during pasting.(Ultra-sound vibrating plate manufactured by Skymen Cleaning EquipmentShenzhen Co. Ltd was used, current rating on the US plate used was 1.75A, and the electrode was placed covering one transducer point on theplate). The pasted electrode was turned over a couple of times while theultra-sound was in operation until a smooth distribution of paste on thesurface was observed where the majority of paste had penetrated to thefelt.

The total amount of wet mass loaded into the electrode was 24. 62 gwhere the achieved capacity (low current discharging) was 3.077 Ah (i.e.62% of the theoretical capacity). The pasted electrode active area(pasted) dimensions were, length 59 mm, width 45 mm, and thickness 2.7mm. The achieved lead loading per volume (pasted density of theelectrode based on the mass loaded into the electrode) was 2.63 g/cm³.At the fully charged state of the electrode, active mass Pb to carbonvolume ratio is 4.52. The average spacing between carbon fibres wasabout 40 microns.

Subsequently the electrode was air-dried for 24 hours at ambienttemperature (18° C.-24° C.) and then the pasted electrode was assembledin a cell containing electrolyte of 1.15 sg H₂SO₄ with one (40% SOC)positive electrode on each side. The cell was left soaking for 24 hoursat ambient temperature (18° C.-24° C.). Then formation charging andstabilisation was carried out similarly as for example 1.

Tests and Results: The cells were then transferred to carry out standardcranking tests (CCA) both at room temperature and −18° C. using the SAEJ537 test as known in the industry.

Example 5—Non-Composite Electrode of Arc Treated Carbon Felt with anAdditional Current Collector of Lead Coated Copper Wires on Felt Surface(Approximately 1 m in Total Length) Active Mass/Carbon Volume Ratio˜3.63-N411˜see FIGS. 1 and 13

Method: An electrode was constructed of carbon fibrous layers ofarc-treated carbon felt (Sigracell KFD2.5 EA manufactured by SGL CarbonCompany, Germany). The felt was treated in an electric arc generally aspreviously described with reference to FIGS. 8 and 9. The felt beforearc-treatment had a specific weight of 248 g/m², thickness of 2.5 mm,and carbon volume fraction ˜7%. The material post arc-treatment had 190g/m² specific weight, was 2.24 mm thick, and had ˜6% carbon volumefraction.

Lead coated Cu wires of 0.38 mm in diameter were used as an additionalcurrent collector for the above electrode. These were laid on the feltsurface manually along the length of the felt in a zig-zag manner wherethe vertical strips were evenly spaced along the width.

Preparation of paste and pasting was as described above for N363 exceptthat an US time of 1 min 17 s was used.

The total amount of wet mass loaded in to the electrode was 17.08 gwhere the achieved capacity (low current discharging) was 2.15 Ah (i.e.67.7% of the theoretical capacity). The pasted electrode active area(pasted) dimensions were, length 60.5 mm, width 44.1 mm, and thickness3.6 mm. The achieved lead loading per volume (pasted density of theelectrode based on the mass loaded on to the electrode) was 1.28 g/cm³.At the fully charged state of the electrode, active mass Pb to carbonvolume ratio is 3.63. The average spacing between carbon fibres wasabout 40 microns.

Subsequently the electrode was air-dried for 24 hours at ambienttemperature (18° C.-24° C.) and then the pasted electrode was assembledin a cell containing electrolyte of 1.15 sg H₂SO₄ with one (40% SOC)positive electrode on each side. The cell was left soaking for 24 hoursat ambient temperature (18° C.-24° C.). Then formation charging andstabilisation was carried out similarly to example 1.

Tests and Results: The cell was then transferred to do cranking amperetests at room temperature prior to sending for water consumption testing(Tafel). The standard Tafel test is described in Fernandez, M.,Atanassova, P., ALABC Project ref 1012M report no. 1, March-August 2011.

Example 6—Non-Composite Electrode of Arc Treated Woven Carbon Fibre,Active Mass/Carbon Volume Ratio ˜0.88-N305—see FIG. 14

Method: An electrode was constructed of woven carbon fibre fabric PAN[polyacrylonitrite] based woven carbon fibre tape (manufactured byTaiCarbon, Taiwan). The fabric was treated in an electric arc generallyas previously described with reference to FIGS. 8 and 9. Thisarc-treated fabric had 181 g/m² specific weight, was 0.58 mm thick, andhad ˜18.4% carbon volume fraction. Four pieces of the arc-treated fabricwere cut into the size of 44 mm*70 mm.

Prior to arc treatment the material was fully wetted with Pb (NO₃)₂aqueous solution, and dried overnight so that 2 mass % Pb was deposited.

Four such layers were then assembled one beneath the other so that theywere all bonded to lead shim to form a connecting lug at one of theirends. 15 mm*44 mm pieces of solder flattened (50% Sn, 50% Pb) wereplaced in the three gaps between the four layers and also two on the twoouter surfaces. A 25 mm wide ribbon of metallic lead (0.6 mm thick) wasthen wrapped around the outside of the ends of the four layers, coveringthe top 10 mm section of each layer. This construction was placed in ametallic box under inert air condition (box filled with nitrogen) andplaced in an oven for ˜1 hour under 200° C. The lead coverings weresqueezed after taking out from the oven providing good contact betweenthe carbon fibres and molten solder and lead. In this way, a lug wasformed on the top end of the electrode, connecting and holding thecarbon fabric layers that could be flexibly moved about for furthertreatment.

To make the active material, PbSO₄ powder (mean size 4-5 μm aftermilling) was mixed in with low concentration sulphuric acid (s.g. <1.05)to make a paste of 77.3 mass % PbSO₄. The above lug was placed on a flatplate. The lug was placed on the pasting plate holding the top threelayers up from the plate while the fourth lay flat on the plate. Pastewas applied on the fourth layer on the flat plate. The next layer wasthen released onto the first layer. Paste was distributed on the surfaceof the second layer until achieving a smooth surface. The aboveprocedure was repeated for the next two layers. Then the wholeconstruction was turned over on the plate which was then vibrated withultrasound, which caused the paste to penetrate and distribute evenlyuntil all the fibre spaces were filled up. This was achieved during anultrasound period of around 30 s.

The total amount of wet mass loaded in to the electrode was 15.6 g wherethe achieved capacity (low current discharging) was 2.33 Ah (i.e. 62% ofthe theoretical capacity).

The pasted electrode active area (pasted) dimensions were length 61 mm,width 44.7 mm, and thickness 2.22 mm. The achieved lead loading pervolume (pasted density of the electrode based on the mass loaded on tothe electrode) was 1.402 g/cm³. At the fully charged state of theelectrode, active mass Pb to carbon volume ratio is 0.88. The averagespacing between carbon fibres was about 17 microns.

Subsequently the electrode was air-dried for 24 hours at ambienttemperature (18° C.-24° C.) and then the pasted electrode was assembledin a cell containing electrolyte of 1.15 sg H₂SO₄ with one (40% SOC)positive electrode on each side. The cell was left soaking for 24 hoursat ambient temperature (18° C.-24° C.). Then formation charging andstabilisation was carried out similarly to example 1.

Tests and Results: The cell was then transferred to do cranking amperetests at room temperature prior to sending for water consumption testing(Tafel) as for electrode 411. The standard Tafel test is described inFernandez, M., Atanassova, P., ALABC Project ref 1012M report no. 1,March-August 2011.

Example 7—Non-Composite Electrode of Arc Treated Carbon Felt, ActiveMass/Carbon Volume Ratio ˜2.63-N356—see FIG. 16

Method: An electrode was constructed of carbon fibrous layers ofarc-treated carbon felt (Sigracell KFD2.5 EA manufactured by SGL CarbonCompany, Germany). The felt was treated in an electric arc generally aspreviously described with reference to FIGS. 7 and 8. The felt beforearc-treatment had a specific weight of 248 g/m², thickness of 2.5 mm,and carbon volume fraction ˜7%. The material post arc-treatment had 217g/m² specific weight, was 2.47 mm thick, and had ˜6.3% carbon volumefraction.

Preparation of paste and pasting was as described above for N363 exceptthat an US time of 1 min 26 s was used.

The total amount of mass loaded in to the electrode was 15.60 g wherethe achieved capacity (low current discharging) was 1.93 Ah (i.e. 67% ofthe theoretical capacity). The electrode active area (pasted) dimensionswere, length 61.02 mm, width 44.77 mm, and thickness 2.34 mm. Theachieved lead loading per volume (pasted density of the electrode basedon the mass loaded on to the electrode) was 1.75 g/cm³. At the fullycharged state of the electrode, active mass Pb to carbon volume ratio is2.63. The average spacing between carbon fibres was about 37 microns.

Subsequently the electrode was air-dried for 24 hours at ambienttemperature (18° C.-24° C.) and then the pasted electrode was assembledin a cell containing electrolyte of 1.15 sg H₂SO₄ with one (40% SOC)positive electrode on each side. The cell was left soaking for 24 hoursat ambient temperature (18° C.-24° C.). Then formation charging andstabilisation was carried out similarly to example 1.

Tests and Results: The cell was then transferred to do cranking amperetests at both room temperature and −18 C prior to being sent for HR-DCATtesting. The results are shown in table 2 and FIG. 16.

Example 8—Non-Composite Electrode of Arc Treated Carbon Felt, ActiveMass/Carbon Volume Ratio ˜3.68-N409

Method: An electrode was constructed of carbon fibrous layers ofarc-treated carbon felt (Sigracell KFD2.5 EA manufactured by SGL CarbonCompany, Germany). The felt was treated in an electric arc generally aspreviously described with reference to FIGS. 8 and 9. The felt beforearc-treatment had a specific weight of 248 g/m², thickness of 2.5 mm,and carbon volume fraction ˜7%. The material post arc-treatment had 183g/m² specific weight, was 1.98 mm thick, and had ˜6.6% carbon volumefraction.

Lead coated copper wires of 0.38 mm in diameter were used as anadditional current collector for the above electrode. These were laid onthe felt surface manually along the length of the felt in a zig-zagmanner so that the vertical strips were evenly spaced along the widthprior to injecting the lug. The lug was injected onto the felt in amanner that the top (zag) of each line of the wire attached to the lug.

Preparation of paste and pasting was as described above for N363 exceptthat an US time of 1 min 10 s was used.

The total amount of wet mass loaded in to the electrode was 17.79 gwhere the achieved capacity (low current discharging) was 2.03 Ah (i.e.61% of the theoretical capacity). The electrode active area (pasted)dimensions were, length 63.5 mm, width 44.85 mm, and thickness 2.71 mm.The achieved lead loading per volume (pasted density of the electrodebased on the mass loaded on to the electrode) was 1.66 g/cm³. At thefully charged state of the electrode, active mass Pb to carbon volumeratio is 3.68. The average spacing between carbon fibres was about 45microns.

Subsequently the electrode was air-dried for 24 hours at ambienttemperature (18° C.-24° C.) and then the pasted electrode was assembledin a cell containing electrolyte of 1.15 sg H₂SO₄ with one (40% SOC)positive electrode on each side. The cell was left soaking for 24 hoursat ambient temperature (18° C.-24° C.). Then formation charging andstabilisation was carried out similarly to example 1.

Tests and Results:—The cells were then transferred to test for standardcranking test at room temperature prior to sending for HR-DCAT testing.The results are set out in table 2 and FIG. 15.

Example 9—Non-Composite Electrode of Arc Treated Carbon Felt with anAdditional Current Collector of Lead Coated Copper Wires on Felt Surface(Approximately 1 m in Total Length), Active Mass/Carbon Volume Ratio˜3.797-N410—see FIG. 18

Method: An electrode was constructed of carbon fibrous layers ofarc-treated carbon felt (Sigracell KFD2.5 EA manufactured by SGL CarbonCompany, Germany). The felt was treated in an electric arc generally aspreviously described with reference to FIGS. 8 and 9. The felt beforearc-treatment had a specific weight of 248 g/m², thickness of 2.5 mm,and carbon volume fraction ˜7.1%. The material post arc-treatment had183 g/m² specific weight, was 1.98 mm thick, and had ˜6.6% carbon volumefraction.

Lead coated copper wires of 0.38 mm in diameter were used as anadditional current collector for the above electrode. These were laid onthe felt surface manually along the length of the felt in a zig-zagmanner where the vertical strips were evenly spaced along the widthprior to injecting the lug. The lug was injected into the felt in amanner that the top of each zag of the Cu wire attached to the lug.

Preparation of paste and pasting was as described above for N363 exceptthat an US time of 1 min 11 s was used.

The total amount of wet mass loaded in to the electrode was 17.66 gwhere the achieved capacity (low current discharging) was 2.11 Ah (i.e.64.4% of the theoretical capacity). The pasted electrode active area(pasted) dimensions were, length 61.71 mm, width 44.34 mm, and thickness2.78 mm. The achieved lead loading per volume (pasted density of theelectrode based on the mass loaded on to the electrode) was 1.67 g/cm³.At the fully charged state of the electrode, active mass Pb to carbonvolume ratio is 3.797. The average spacing between carbon fibres wasabout 45 microns.

Subsequently the electrode was air-dried for 24 hours at ambienttemperature (18° C.-24° C.) and then the pasted electrode was assembledin a cell containing electrolyte of 1.15 sg H₂SO₄ with one (40% SOC)positive electrode on each side. The cell was left soaking for 24 hoursat ambient temperature (18° C.-24° C.). Then formation charging andstabilisation was carried out similarly to example 1.

Tests and Results: The cells were transferred to submit them to standardcranking test at room temperature prior to sending for Axion-DCAtesting.

Example 10—Non-Composite Electrode of Arc Treated Carbon Felt(Thickness˜1.3 mm) with an Additional Current Collector of Lead CoatedCopper Wires on Felt Surface (Approximately 1 m in Total Length), ActiveMass/Carbon Volume Ratio ˜4.893-N441—see FIG. 1

This electrode was constructed with carbon fibrous layers usingarc-treated felt JX-PCF, manufactured by Heilongjiang J&X Co., Ltd.China. The felt had a specific weight of 508 g/m², thickness of 4 mm andcarbon volume fraction ˜7.5%. The material was splitted in to a thinnerstrip (manually cutting using a sharp blade) and arc-treated asexplained in previous examples. Post arc-treatment had 144 g/m² specificweight, was 1.3 mm thick, and had ˜6.4% carbon volume fraction.

Lead coated Cu wires-0.38 mm in diameter were used as an additionalcurrent collector for the above electrode. These were laid on the feltsurface manually along the length of the felt in a zig-zag manner withthe vertical strips evenly spaced along the width, prior to putting alug on. The lug was prepared for this electrode in the same manner asexplained in the example 5 above using solder (50% Sn and 50% Pb) makingsure that top of each zag of the Cu wire was immersed in the lug andattached to the lug.

Preparation of paste and pasting was as described above for N363 exceptthat an US time of 1 min 48 s was used.

The total amount of wet mass loaded into the electrode was 16.11 g wherethe achieved capacity (low current discharging) was 2.052 Ah (i.e. 63%of the theoretical capacity). The pasted electrode active area (pasted)dimensions were, length 59.8 mm, width 44.9 mm, and thickness 1.78 mm.The achieved lead loading per volume (pasted density of the electrodebased on the mass loaded into the electrode) was 2.64 g/cm³. At thefully charged state of the electrode, active mass Pb to carbon volumeratio is 4.893. The average spacing between carbon fibres was about 23microns.

TABLE 2 Utilization % of discharged capacity on theoretical capacity NAMPb loading Vol Vol Pb:C based on NAM loaded Electrode loaded per volfraction fraction Electrode vol 1^(st) 2^(nd) Electrode material (gm)(gm/cm3) of C of Pb voidage fraction Discharge Discharge N356 Felt arc15.60 1.75 0.06 0.16 0.79 2.63 72 67 treated (2.09 Ah) (1.93 Ah) N363Felt arc 19.50 1.91 0.06 0.17 0.77 2.70 72 66 treated (2.60 Ah) (2.39Ah) N349 Woven - 14.87 1.72 0.18 0.15 0.67 0.83 69 60 arc- (1.91 Ah)(1.65 Ah) treated N439 Felt arc 24.62 2.63 0.05 0.23 0.72 4.52 67 62treated (3.35 Ah) (3.08 Ah) N305 Woven - 15.58 1.36 0.19 0.17 0.64 0.8867 55 arc- (1.43 Ah)  (1.2 Ah) treated N409 Felt arc 17.79 1.66 0.040.15 0.81 3.68 65 61 treated  (2.1 Ah) (2.03 Ah) N410 Felt arc 17.661.67 0.04 0.15 0.81 3.797 72 64 treated (2.36 Ah) (2.11 Ah) N411 Feltarc 17.68 1.33 0.03 0.11 0.86 3.63 74 65 treated (2.44 Ah) (2.15 Ah)N441 Felt arc 16.11 2.64 0.05 0.23 0.72 4.893 65 63 treated (2.12 Ah)(2.05 Ah)

Example 11—Non-Composite Electrode of Arc Treated Carbon Felt, ActiveMass/Carbon Volume Ratio ˜2.53-N387

Method: An electrode was constructed of carbon fibrous layers ofarc-treated carbon felt Sigracell KFD2.5 EA manufactured by SGL CarbonCompany, Germany). The felt was treated in an electric arc generally aspreviously described with reference to FIGS. 8 and 9. The felt beforearc-treatment had a specific weight of 248 g/m², thickness of 2.5 mm,and carbon volume fraction ˜7%. The material post arc-treatment had 203g/m² specific weight, was 2.25 mm thick, and had ˜6.4% carbon volumefraction.

Preparation of paste and pasting was as described above for N363 exceptthat the vanisperse A™ solution was prepared in order to achieve 0.07/0in mass of Vanisperse A™ in the final paste and an US time of 1 min 23 swas used.

The total amount of wet mass loaded in to the electrode was 14.2 g wherethe achieved capacity (low current discharging) was 1.68 Ah (i.e. 64% ofthe theoretical capacity).

The pasted electrode active area (pasted) dimensions were length 67.4mm, width 44.8 mm, and thickness 2.46 mm. The achieved lead loading pervolume (pasted density of the electrode based on the mass loaded on tothe electrode) was 1.38 g/cm³. At the fully charged state of theelectrode, active mass Pb to carbon volume ratio was 2.53. The averagespacing between carbon fibres was about 39 microns.

Subsequently the electrode was air-dried, assembled in a cell, the cellwas left soaking, and then formation charging was carried out in thecell, all as described in example 1. Then the cell was transferred tocarry out the standard cranking ampere tests on room temperature and−18° C.

Example 12—Non-Composite Electrode of Arc Treated Carbon Felt, ActiveMass/Carbon Volume Ratio ˜2.696-N392

Method: An electrode was constructed of carbon fibrous layers ofarc-treated carbon felt Sigracell KFD2.5 EA manufactured by SGL CarbonCompany, Germany). The felt was treated in an electric arc generally aspreviously described with reference to FIGS. 7 and 8. The felt beforearc-treatment had a specific weight of 248 g/m², thickness of 2.5 mm,and carbon volume fraction ˜7%. The material post arc-treatment had 203g/m² specific weight, was 2.25 mm thick, and had ˜6.4% carbon volumefraction.

Preparation of paste and pasting was as described above for N363 exceptthat the Vanisperse A™ solution was prepared in order to achieve 0.25%in mass of Vanisperse A™ in the final paste and an US time of 1 min 23 swas used.

The total amount of wet mass loaded in to the electrode was 15.33 gwhere the achieved capacity (low current discharging) was 1.83 Ah (i.e.64% of the theoretical capacity).

Example 13—Amount of Sulphuric Acid Used in Paste

A small batch of paste made up of a suspension of particles of leadmonoxide (97 mass %) and lead (3%) together with water, and increasingamounts of acid were added. The 13.0 g of solid was suspended in 3.65 gof water, achieving a solids mass fraction of 78% and volume fraction ofaround 27%. This was a freely settling slurry, difficult to keepuniformly suspended, and difficult to evenly spread onto a felt layer.Vibration (ultrasound) did not improve the properties and did not bringabout easy penetration. The pH of the liquid in equilibrium with thesolids was 10. Small amounts of acid were added to bring the acid toaround 0.12 mass % when a slight creaminess was observed, and the pH wasaround 9 to 9.5. A further addition to 0.5% resulted in a creamy pasteand a pH of 8.5 to 9. Addition of further acid brought the pH down to abuffered 8.0.

Several separate mixes were then made with the same solids fraction asabove, and dispersion and penetration through felt via ultrasound wasattempted for succeeding higher acid concentrations. At 0.24 mass %acid, there was little stability of the paste mass on a spatula, but thepaste penetrated well (some appeared at the other side of a 2.3 mm thickfelt). The optimum acid addition was around 1.0% when both penetrationand high loading of the felt was possible. As the acid was increased thepaste became stiffer with paste at 2.28% being able to be pasted with aspatula but much of it remained on the outside of the felt layer afterultrasound with poor penetration and rapid drying.

The foregoing describes the invention including preferred forms thereofand alterations and modifications as will be obvious to one skilled inthe art are intended to be incorporated within the scope hereof asdefined in the accompanying claims.

The invention claimed is:
 1. A lead-acid battery or cell including atleast one electrode comprising as a non-composite current collector acarbon fibre material, and an active mass, the active mass supported atleast predominantly by the carbon fibre material, the carbon fibrematerial having a carbon fibre volume fraction of less than 40%, and theelectrode having a loading ratio of the volume of lead in the activemass to the volume of carbon fibres greater than 0.5 to about 15:1, eachover at least a major fraction of the electrode, and/or at least oneelectrode comprising as a composite current collector a metal grid and acarbon fibre material, and an active mass in the metal grid and carbonfibre material with at least 20% of the active mass in the carbon fibrematerial, the carbon fibre material having a carbon fibre volumefraction of less than 40%, and the electrode having a loading ratio ofthe volume of lead in the active mass to the volume of carbon fibresgreater than 0.5 to about 15:1, each over at least a major fraction ofthe electrode.
 2. A lead-acid battery or cell according to claim 1having a carbon fibre volume fraction of less than 30%, and a loadingratio of the volume of lead in the active mass to the volume of carbonfibres greater than 0.7 to about 15:1.
 3. A lead-acid battery or cellaccording to claim 1 having a carbon fibre volume fraction of less than20%, and a loading ratio of the volume of lead in the active mass to thevolume of carbon fibres greater than 1:1 to about 10:1.
 4. A lead-acidbattery or cell according to claim 1 wherein the active material alsocomprises an expander.
 5. A lead-acid battery or cell according to claim1 wherein the electrode comprises said metal grid and the carbon fibrematerial comprises a single layer on one side of the metal grid.
 6. Alead-acid battery or cell according to claim 1 wherein the electrodecomprises said metal grid and the carbon fibre material comprisesmultiple layers at least on either side of the metal grid.
 7. Alead-acid battery or cell according to claim 1 wherein the electrodecomprises said metal grid and at least 20% of the active mass is in thecarbon fibre material.
 8. A lead-acid battery or cell according to claim1 wherein the electrode comprises said metal grid and at least 40% ofthe active mass is in the carbon fibre material.
 9. A lead-acid batteryor cell according to claim 1 wherein the electrode comprises said metalgrid and at least 60% of the active mass is in the carbon fibrematerial.
 10. A lead-acid battery or cell according to claim 1 whereinthe electrode comprises said metal grid and not more than 80% of theactive mass is in the carbon fibre material.
 11. A lead-acid battery orcell according to claim 1 wherein the electrode has a thicknesstransverse to a length and width or in plane dimensions of the electrodeof less than 5 mm.
 12. A lead-acid battery or cell according to claim 1wherein the electrode has a thickness transverse to a length and widthor in plane dimensions of the electrode of less than 3 mm.
 13. A hybridautomotive vehicle comprising a battery according to claim
 1. 14. Ahybrid automotive vehicle according to claim 13 which has stop-startfunctionality.
 15. A hybrid automotive vehicle according to claim 14wherein the battery carries accessory loads when an engine of the hybridautomotive vehicle is off.